The traditional DC to DC Converter is applied to adjust the voltage level of the DC input voltage to stabilize the output voltage at a pre-determined value.
Please refer to FIG. 1, it is a block diagram showing the circuit configuration of the prior art of the present invention. Mainly, this circuit configuration is used to offer a constant frequency from a resistance-capacitance oscillator (RCO) 10 to a pulse width modulation (PWM) circuit 11 to engage in the modulation. Thus, a switching frequency signal Fp is generated to control a controllable switch 12 which is made of an n-type metal-oxide-semiconductor transistor (NMOS) to maintain the output voltage at a certain value.
The method to control the switch frequency signal Fp is as follows:
1. When the Fp is at the high level, the switch 12 is conducted. Through the inductor L, the input current IL flows through NMOS, then IL is grounded. Thus, the diode D is reverse-biased, and an output current is offered by the capacitor C onto the load RL.
2. When Fp is at the low level, the controllable switch 12 is closed. The inductor L will change the direction of the magnetic field thus making the positive pole and negative pole of the inductor to switch. This will cause the diode D to be forward-biased, and make the energy store in the inductor to produce an output current. Through the diode D, the output current is offered onto the load RL.
Please refer to FIG. 2, which is a plot showing that through the switching frequency signal Fp to control the controllable switch 12 will cause the variance of the current flowing through the inductor. It can be seen from the plot, when Fp is at the high level, the inductor L is in the charging status thus the current IL will keep on increasing. When Fp is at the low level, the energy stored in the inductor L will produce an output current onto the load RL thus the current IL will keep on decreasing.
Since the current flowing through the inductor is changing, this will make the inductor to produce a magnetic field. In the application of the wireless communication system, this magnetic field will interfere with the reception of the Radio Frequency (RF), and cause the deteriorating of the sensitivity of the receiving signals or the receiving information.
Keep the drawbacks of the prior art in mind, and employ experiments and research full-heartily and persistently, the method and the circuit for controlling switching signals are finally conceived by the applicants.